My newest kit-bash creation - a skaven 'super-mortar' / 'uberweapon' (name tbc).
I stupidly deleted most of the photos of the earliest stages when I was trying to create space on my phone (for the later pictures ... doh!) but two survived.
Here you can see an early test to see how it might fit together ...

It was given to me already glued together, and would have been impossible to paint what with all the inaccessible innards. So I hacked it apart and began a-bashing. Here are the pieces undercoated ...

There is a standard doomsphere, a toy cannon (Playmobile?) and various other bits, including wheels.
Now here are the pics of the completed model from various angles ...






Gibby, of this fine forum, is the Skaven player in the campaign. He and I are going to have to come up with rules for the machine.
The general idea I have so far is that this is Clan Skryre's attempt to create an army or city-destroyer. Inside the huge iron barrel is a warpstone grenado far bigger and far more potent than the bombs thrown by poisoned wind globadiers. The engine is mechanised (a converted doom wheel) to ensure it moves at speed, as it has to get within range of its target to lob the warpstone bomb, without being destroyed by enemy artillery or troops. Being a skaven engine it is unreliable, so it could blow up, centering it's table-sized blast radius on itself! If it succeeds in lobbing it's bomb, then a city could die! No damage to the buildings, but all life (give or take a few very lucky survivors) perishes. The globe is fused to blow in the air above the city. I might make that fact one of things that could go wrong, as if it hits the ground it will have a much, much lesser effect.
I reckon we can have a brilliant scenario game in which the skaven player has to get this intact from one side of the board to the other. If he does so, then we roll for it firing. If that goes wrong, everything on the table could die!
I have ordered the sprues for 10 plague monks which I am gonna convert (masking them up) to be this engine's attendants.